The present invention relates to methods for managing storage of data in a composite non-volatile memory that is a composite of a slow memory device and a fast memory device. In a composite disk system, a large, slow, and inexpensive magnetic hard drive can be combined with a small, fast but expensive storage device, such as a solid state drive to form a logical volume. This can provide the advantage of fast access through the solid state drive (SSD) while providing the large capacity of the magnetic hard disk drive (HDD). Prior techniques for managing such a composite disk have used algorithms such as a least recently used (LRU) algorithm or a CLOCK algorithm or the ClockPro algorithm described by Song Jiang. These prior techniques can improve the allocation of the data between the fast and the slow portions of the composite disk, but they tend to not be space efficient, in that they require large amounts of main memory, such as large amounts of DRAM, in order to implement the data structures used in these techniques for allocating data between the two parts of the composite disk. Hence there is a need for an improved, space efficient technique, which does not require as much memory to store the data structures used in allocating or migrating data between the two or more components of the composite disk.